The maximum donation to the presidential trust, said Scaramucci, is $33,400, so Trump would need about 15,000 donors contributing the max amount.

Scaramucci said that he factored in Trump's wide appeal in concluding that Trump would only need to spend half of what Mitt Romney did.

"He is a force of nature. He's got an unbelievable personality. He's got probably the best name-brand recognition. He's also a ratings machine. We know that," he explained, adding that Trump could always end up going over the billion.

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